In various settings, relatively precise steering of vehicles may be important. For example, in agricultural settings it may be important to precisely steer an agricultural vehicle across a field in order to seed, tend, harvest, or otherwise process crops or other material.
In certain vehicles, the configuration of one set of wheels may vary from the configuration of another set of wheels. For example, in various combines, windrowers, or other vehicles, a rear set of wheels may be mounted on casters, whereas a forward set of wheels may be mounted to a fixed axle (or axles). In certain embodiments, the forward wheels may be fixed in a forward-facing orientation (i.e., may not be configured to turn to the sides to steer the vehicle). In such a configuration, the vehicle may be steered at the front wheels by driving the front wheels at different speeds from each other. For example, a dedicated hydraulic machine (e.g., a dedicated hydraulic pump) may be provided for each of the front wheels, such that each wheel may be driven independently of the other.
It may be useful to provide a system to control the steering of both the front and the rear wheels of these types of vehicles, as well as the wheels of vehicles having various other configurations. Known steering control methods may include, for example, the use of a rack and pinion arrangement that is mechanically connected to a steering input device (e.g., a steering wheel), an Ackermann linkage, or another mechanical device. As the steering input device is moved by an operator, this may mechanically rotate the pinion with respect to the rack, thereby mechanically driving movement of the rack (or otherwise move the relevant mechanical device). The movement of the rack (or other device) may in turn, for example, control steering of a set of front wheels or a set of rear wheels. With regard to the rear wheels, for example, the mechanical movement of the rack and pinion may mechanically port flow of hydraulic fluid to hydraulic cylinders at the rear of the vehicle, in order to control steering of a set of rear wheels.